He found that the Bible far outsold any other book, with a whopping 3.9 billion copies sold over the last 50 years. "Quotations from the Works of Mao Tse-tung" came in second with 820 million copies sold, and "Harry Potter" came in third with 400 million copies sold.

Designer Jared Fanning created an infographic (below) on the most read books in the world, based on Chapman's research.